The 60 GHz band is an unlicensed band which features a large amount of bandwidth and a large worldwide overlap. The large bandwidth means that a very high volume of information can be transmitted wirelessly. As a result, multiple applications that require transmission of a large amount of data can be developed to allow wireless communication around the 60 GHz band. Examples of such applications include, but are not limited to, wireless high definition TV (HDTV), wireless docking stations, wireless Gigabit Ethernet, and many others. Wireless local area network (WLAN) standards, such as WiGig Alliance (WGA) and IEEE 802.11ad, are being developed to serve applications that utilize the 60 GHz spectrum.
In wireless communication systems such as the one described above, different operational modes are defined for the operation of the modem. Each operational mode is designed for a different scenario of the communication channel between a receiver and a transmitter in the communication system. That is, each scenario is typically related to a signal-to-noise ratio (SNR) or to a signal-to-interference ratio of the channel between the transmitter and receiver. The scenario may also be defined with regard to other parameters, such as temperature, amplifier stability, and the like.
The use of multiple modes allows a modem to be used in many scenarios, including some scenarios where the radio link throughput can be decreased (while reliability is maintained) when compared to other possible scenarios. Examples of those situations include, but are not limited to, a scenario where the SNR is 30 dB and, for comparison, a scenario where the SNR is 0 dB. In such a scenario, the difference in the received power levels in the receiver input is 1000 times. Such degradation in the SNR in most wireless communication systems is due to a decrease in the signal power, which in turn is due to either the effect of longer transmitter-receiver distance, or the effect of fading or shadowing.
The operational modes in most wireless communication modems are composed of two parameters: a constellation configuration and an error-correcting code rate. Some examples of possible constellation configurations are binary phase shift keying (BPSK), Quadrature Phase Shift Keying (QPSK), 16-Quadrature amplitude modulation (16-QAM), 64-QAM, spread-spectrum, and the like. Some examples of possible coding rates are ¼, ½, ⅝, ¾, and the like. These operational modes are referred to as Modulation and Coding Schemes (MCSs).
In millimeter-wave communication systems, such as that defined by the IEEE 802.11ad standard published Dec. 28, 2013 (hereinafter the IEEE 802.11ad standard), the high degradation due to the high frequency of the carrier signal is usually mitigated by using a small size array of antennas realized by small size antenna elements. Such an antenna array focuses the beam of the transmitting and receiving antennas, such that the transmitter-receiver channel's SNR or signal-to-interference, together with the noise on the channel, is maximized. This optimization depends on the physical locations of the transmitter, the receiver, and other objects located between the receiver and the transmitter.
In conventional wireless communication systems and, in particular, in systems that currently implement the IEEE 802.11ad standard, the decision regarding which MCS to be utilized is based on a trial-and-error process in which several MCSs (code rates and constellations) are tested, and the operational mode with the best performance is selected. However, because the physical channel changes from time to time, different codes should be used over time. Thus, the MCS selection process is re-performed when a new MCS needs to be selected.
A common conventional practice is to use a rate-scaling (or so-called link adaptation) process to obtain a reliable link. In the related art, when the transmitter detects a degradation in the channel reliability, the transmitter resorts to rate scaling to improve reliability, which typically also decreases the throughput. However, in some situations, for example, in the case of interferences, the throughput is actually increased.
A conventional rate selection process for restoring the channel reliability as commonly utilized by a millimeter-wave communication system 10 is shown in FIG. 1. As noted above, such a communication system typically includes an antenna array with a plurality of elements. In the conventional process, an antenna training process (S12) is performed first. An antenna (or beam-forming) training process is a bidirectional sequence of beam-forming training frame transmissions that provides the necessary signaling to allow each wireless station to determine appropriate antenna system settings for both transmission and reception antennas.
As shown in FIG. 1, following the antenna training, a rate-scaling process (S14) is utilized by the transmitter. Using the rate scaling process (S14), a proper modulation and coding scheme (MCS) can be used by the transmitter upon completion of the antenna array training. In sum, the antenna array training process (S12) and rate scaling process (S14) are alternately performed to establish a reliable communication link between the transmitter and receiver, each of which separately attempts to maximize the channel and communication system throughput.
In the rate-scale mode of operation (S14), whenever the transmitter detects a drop in the reliability of the link (channel), the transmitter decreases the throughput by changing the MCS, and then continues to operate the link. In some cases, when the error bit rate is burst, increasing the MCS can improve the link throughput. If no reliable link is obtained, even in an instance when the lowest MCS is selected, the rate-scaling sub-process (S14) stops, and the millimeter wave antenna arrays are re-trained to allow a better link.
Once a reliable link is re-established, conventional techniques try to find the best MCS by increasing the rate, while keeping a reliable radio link. The conventional techniques suffer from various drawbacks, such as requiring a longer period of time to obtain a reliable radio link. This is mainly because, first, in the current conventional techniques, all of the available MCSs are tried, and only after all MCSs have been tested is re-training of the antennas performed. In addition, upon obtaining the link through the antenna training, the last workable MCS is utilized, which results in long convergence times before the correct MCS may be identified (stationary rate-scale algorithm). Further, conventional rate scaling techniques typically result in sub-optimal links, as the rate-scaling (S14) finds a workable MCS despite the link degradation.
Therefore, it would be advantageous to provide a rate selection solution for millimeter-wave communication systems that overcomes the above-noted deficiencies.